Excellent entry!!! and great topic.
Actually it was not so much a matter of using any weapon they could get, as being the arms of many tribal groups from regions in proximity and areas which had been sources for slaves. As noted the Zande were perhaps with tribesmen of many other groups who became in effect 'conscripted' into the army of the Caliph basically in place of the slave potential.
It is amazing that so many weapon forms from these other regions were found and often, if not typically, covered in thuluth. These post dated the death of the Mahdi (1885) I believe, and the techniques as well as many weapons and armor may have come from Mamluk origins in some degree. It seems in effect that tribesmen familiar with their indigenous weapons would fight better with their own weapons, and being imbued with the Mahdi's phrases would add to the fervor in their drive in battle.
While it is possible that Indian mail was present in some cases, again there were examples from Mamluk origins, and with that some Sudanese who could produce mail (Arkell). There was a good deal of mail captured or obtained from the Egyptian forces of the Khedive, whose coats were actually produced in Birmingham, and the British may have supplied helmets as well.
The mail was however not especially favored as it would shatter and actually compound wounding potential becoming shrapnel in addition to the round.
I get carried away with this topic, but its been something that has had me preoccupied with this history for many years
